Process and apparatus for bending tubes to small radii



Sept. 21, 1954 T 2,689,596

PROCESS AND APPARATUS FOR BENDING TUBES TO SMALL RADII Fil'd May 13, 1949 INVENTOR;

A Ian/DRE H067 I Patented Sept. 21,1954

PROCESS AND APPARATUS FOR BENDING TUBES T SMALL RADII Andr Huet, Paris, France, assignor to Combustion Engineering, Inc.

poration of Delaware New York, N. Y., a cor- Application May 13, 1949, Serial No. 92,994

3 Claims.

This invention relates to a process for bending or arching of tubes into hairpin loops so as to obtain an inside radius of curvature which is very small with respect to the diameter of the tube. It applies particularly to cases where the inside radius of curvature is less than 1% times the outside diameter of the tube.

A bend made in accordance with this invention is such that the wall thickness of the tube along the outside radius is not reduced or at most only slightly reduced.

The method according to the invention consists in creating a difference in temperature in such a way that the material along the inside radius is at an appreciably higher temperature than the material along the outside radius, during which time the tubing to be bent is encased in a mold of several pieces, the parts of which are forced together to produce the desired shape.

The material along the inside radius of the bend, hereinafter called the crotch, is heated to a higher temperature and consequently is softer than the material along the outside radius. The latter material therefore offers a greater resistance to deformation during the bending operation so bending can be completed with little or no stretching of this portion of the tube, the change in length that necessarily attends this bending operation being accomplished by a shortening or upsetting of the softer material along the inside radius.

The invention will be best understood upon consideration of the following detailed description of an illustrative embodiment thereof when read in conjunction with the accompanying drawing in which:

Figure 1 shows in plan a tube preliminarily arched on a large diameter and disposed in the mold according to the invention;

Figure 2 is a section on the line 22 of Figure 1;

Figure 3 is a plan view of Figure 1;

Figure 4 is a view, partly schematic, showing the begimiing of the operation with a bend previ ously formed to a larger diameter disposed in the mold;

Figure 5 shows the position of the mold after arching has given to the bend its final form;

Figure 6 shows in section the bend obtained in accordance with the invention.

In order to accomplish a bend of very small radius of curvature, a bend A (Figures 1 and 4) having an ordinary radius of curvature is made first by any desired process, the bend being made with a radius of curvature sufficiently large that there is no appreciable thinning of the tube wall along the outside radius nor flattening through decreaseof outside diameter of the tube in the direction from the inside to the outside radius.

The bend A thus obtained is placed between two plates of metal [0 and II solidly assembled and maintained at a spacing corresponding to the outside diameter of the tube as seen in Figure 2, for example by the use of spacers l2 provided with fastening bolts 13.

A grooved roller 14 is provided between the two plates [0, I l on which the center of the crotch of the bend A is placed as shown in Figures 1 and 4. The radius of the internal groove of roller 14 is equal to the final crotch radius desired. Two laterally sliding blocks or jaws I5 and i6 are mounted between the two plates ill and H in such a manner that they may be moved toward each other between the two said plates in the direction of the arrows B, Figure 1, and inversely. Each of these jaws has a curved face I! conforming to that of the outside curved surface of the final bend. The two jaws I 5 and i6 can be movable or one of them can be fixed and the other movable, but in this latter case the roller- M will also be movable laterally.

The operation of the device is as follows: The

tube A having been bent with a normal radius of curvature is then placed in the device on roller 14 as shown in Figures 1 and 4. At least one flange defining the groove on the roller I4 is provided with a notch l8 as shown in Figures 1 and 4 so that the center portion of the inside radius of the bend A, that portion that is to become the final crotch, is exposed. This exposed portion is then heated by any suitable means, for example with an oxyacetylene fiame, the sides and outer curvature of the bend remaining at a relatively low temperature. When that portion that is to become the crotch is at the proper temperature, the two jaws l5 and 16 are forced together moving them from the position shown in Figure 4 to that shown in Figure 5. During this operation the metal at the crotch, being at a considerably higher temperature than the rest of the tube, and thus more plastic, is upset. Since the metal'along the inner radius a is subject to plastic deformation, the metal along the outer radius b being relatively colder and thus less plastic, bends without tendency to elongate. It may be visualized that since the metal at the crotch c is much more plastic than that along the outside radius 1) of the bend and thus offers practically no resistance to deformation of the tube, the forces introduced by this portion are practically removed from the bending operation, thus the metal along the outside radius 1) of the bend is bent as if it were a single thin sheet which is capable of being bent to a small radius of curvature with practically no thinning of the wall. Since the metal at the crotch c is at a temperature sufficiently high to be quite plastic it is capable of shortening through upsetting without folding because of the uniform progressive compressive action of the dies l5 and It. This compressive action also causes the metal along the inside radius a to conform to the contour of the roller I4 which determines the shape of the crotch. When the operation is completed the bent tube has assumed the shape shown in Figure 6. It will be seen that the tube wall at the crotch c has become thicker, which is an advantage in that it offers greater resistance to deformation during service. It will be seen that the tube wall along the outer radius b is no thinner than it was before bending. The tube within the bent portion has not flattened and thus the internal cross-sectional area is not reduced.

What I claim is:

1. Tube bending apparatus comprising; a mold including a pair of plates maintained in parallel relation at .a spacing'conforming to the external diameter of the tube to be worked on; a bending roller supported between said plates formed with a groove havinga radius of curvature conforming to that desired in the'final bend, said roller being cut away to expose-the crotch region of a tube placedthereon; and a pair of dies relatively movable between said plates toward and away from said roller for engaging straight tubular portions extending from a bend of relatively large radius onsaid roller for reducing the spacing of said portions and compressing the bend.

2. Tube bendingapparatus comprising; a mold including a pair of plates maintained in parallel relation at a spacing conforming to'the external diameter of the tube to be worked on; a bending roller supported between said plates formed with a groove having a radius of curvature conforming to that desired in. the final bend, said roller being cut away to expose the crotch region of a tube placed thereon; and a pair of dies relatively movable between said plates toward and away from said roller for engaging straight tubular portions extending from, a bend of relatively large radius "on said roller for reducing the spacing of said portions and compressing the bend; said dies having confronting faces oppo site said roller that are complementary to the exterior curvature of the final bend for restraining and guiding the tube during reduction of its radius of curvature.

3. The process of forming tube bends whose radius of curvature is less than approximately 1 times the external diameter of the tubing which comprises: bending an empty metallic tube intermediate its ends to form therein an 180 elbow on a radius of curvature sufficiently large that no appreciable thinning occurs in the tube wall along the outside radius and without flattening through decrease of the outside diameter of the tube in the direction from the inside to the outside radius of the bend; heating the empty bend only along its arched internal crotch region over a small central portion thereof hav ing an axis midway between and paralleling the longitudinal axes of the tube legs; with the bend remaining empty, reducing the spacing of the straight tube legs extending from said elbow by applying compressing forces acting in opposite directions in the plane including the longitudinal axes of the tubes through two dies having opposed straight portions which engage with the relatively cold straight leg portions and opposed curved portions shaped to conform with the outside are of the final bend; supporting the internal crotch region of the bend during the application of said compressing forces on a grooved instrumentality conforming to the internal crotch region of the final bend; and, while compressing the empty bend, maintaining the latter confined by restraining members engaging thereagainst at the sides in planes parallel to that containing the longitudinal axes of the tube legs.

References-Cited in the file of this patent UNITED STATES PATENTS Number Name Date 953,253 Brinkman Mar. 29, 1910 2,278,254 Enghauser Mar. 31, 1942 2,373,822 Geppelt Apr. 17, 1945 2,433,055 Linden et al Dec. 23, 1947 FOREIGN PATENTS Number Country Date 106,280 Great Britain Aug. 2, 1917 

